Techniques for supporting relay operation in wireless communication systems

ABSTRACT

Techniques for supporting operation of relay stations in wireless communication systems are described. In an aspect, a base station may transmit data to a relay station in a portion of a subframe instead of the entire subframe. The relay station may transmit control information during part of the subframe. The base station may transmit data to the relay station during the remaining part of the subframe. In another aspect, a target termination for a packet may be selected based on data and/or ACK transmission opportunities available for the packet. One or more transmissions of the packet may be sent with HARQ, and ACK information may be sent for the packet. The packet may be transmitted such that it can be terminated prior to the first subframe (i) not available for sending the packet or (ii) available for sending ACK information.

CLAIM OF PRIORITY

The present application claims priority to provisional U.S. ApplicationSer. No. 61/101,571, filed Sep. 30, 2008, provisional U.S. ApplicationSer. No. 61/101,656, filed Sep. 30, 2008, provisional U.S. ApplicationSer. No. 61/102,337, filed Oct. 2, 2008, and provisional U.S.Application Ser. No. 61/106,917, filed Oct. 20, 2008, all entitled“RELAY OPERATION TECHNIQUES IN LONG TERM EVOLUTION SYSTEMS,” assigned tothe assignee hereof, and incorporated herein by reference.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to concurrently filed and commonly ownedU.S. patent application Ser. No. 12/568,242, entitled “TECHNIQUES FORSUPPORTING RELAY OPERATION IN WIRELESS COMMUNICATION SYSTEMS,” thedisclosure of which is hereby incorporated by reference herein.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for supporting operation of relay stations inwireless communication systems.

II. Background

Wireless communication systems are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast, etc. These wireless systems may be multiple-access systemscapable of supporting multiple users by sharing the available systemresources. Examples of such multiple-access systems include CodeDivision Multiple Access (CDMA) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Orthogonal FDMA (OFDMA) systems, and Single-Carrier FDMA (SC-FDMA)systems.

A wireless communication system may include a number of base stationsthat can support communication for a number of user equipments (UEs).The system may also include relay stations that can improve the coverageand capacity of the system without the need for a potentially expensivewired backhaul link. A relay station may be a “decode and forward”station that may receive a signal from an upstream station (e.g., a basestation), process the received signal to recover data sent in thesignal, generate a relay signal based on the recovered data, andtransmit the relay signal to a downstream station (e.g., a UE).

A relay station may communicate with a base station on a backhaul linkand may appear as a UE to the base station. The relay station may alsocommunicate with one or more UEs on an access link and may appear as abase station to the UE(s). However, the relay station typically cannottransmit and receive at the same time on the same frequency channel.Hence, the backhaul and access links may be time division multiplexed.Furthermore, the system may have certain requirements that may impactthe operation of the relay station. It may be desirable to supportefficient operation of the relay station in light of itstransmit/receive limitation as well as other system requirements.

SUMMARY

Various techniques for supporting operation of relay stations inwireless communication systems are described herein. In an aspect, abase station may transmit data to a relay station in a portion of asubframe instead of the entire subframe. The relay station may transmitcontrol information during part of the subframe. The base station maythen transmit data to the relay station during the remaining part of thesubframe. The base station may process (e.g., encode and interleave) thedata so that it can be reliably received by the relay station.

In another aspect, a target termination for a packet may be selectedbased on data and/or acknowledgement (ACK) transmission opportunitiesavailable for the packet. One or more transmissions of the packet may besent with hybrid automatic retransmission (HARQ), and ACK informationmay be sent for the packet. The transmissions of the packet may be sentin evenly spaced subframes in a first interlace, and the ACK informationmay be sent in evenly spaced subframes in a second interlace. However,only some subframes in the first and second interlaces may be availablefor use due to relay operation. The packet may be transmitted such thatit can be terminated prior to (i) the first subframe not available forsending another transmission of the packet or (ii) the first subframeavailable for sending ACK information (or the first subframe notavailable for sending ACK information, depending on the ACK feedbackdesign).

In yet another aspect, downlink resources may be partitioned into (i)backhaul downlink resources available for a base station to transmit toa relay station and (ii) access downlink resources available for therelay station to transmit to UEs. Similarly, uplink resources may bepartitioned into (i) backhaul uplink resources available for the relaystation to transmit to the base station and (ii) access uplink resourcesavailable for the UEs to transmit to the relay station. The downlinkresource partition may be asymmetric with respect to the uplink resourcepartition, so that the amount of backhaul downlink resources may not beequal to the amount of access downlink resources. The downlink anduplink resource partitions may be selected based on various criteria toobtain good performance.

Various other aspects and features of the disclosure are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIGS. 2 and 3 show exemplary frame structures for frequency divisionduplexing (FDD) and time division duplexing (TDD), respectively.

FIG. 4 shows two exemplary regular subframe formats.

FIG. 5 shows two exemplary MBSFN subframe formats.

FIG. 6 shows an exemplary interlace structure.

FIG. 7A shows data transmission on the downlink via a relay station.

FIG. 7B shows data transmission on the uplink via a relay station.

FIG. 8 shows a bitmap conveying subframes of different types.

FIG. 9 shows symbol timing offset between a base station and a relaystation.

FIG. 10 shows downlink transmissions with new control channels.

FIG. 11 shows communication by a relay station.

FIG. 12 shows data transmission with synchronous HARQ.

FIG. 13 shows subframe timing offset between a base station and a relaystation.

FIG. 14 shows an exemplary asymmetric downlink/uplink partitioning.

FIGS. 15 and 16 show a process and an apparatus, respectively, for datatransmission with target termination selection.

FIGS. 17 and 18 show a process and an apparatus, respectively, for datatransmission in a shortened subframe.

FIGS. 19 and 20 show a process and an apparatus, respectively, foroperation in a wireless communication system.

FIG. 21 shows a block diagram of a base station, a relay station, and aUE.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and othersystems. The terms “system” and “network” are often usedinterchangeably. A CDMA system may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA system may implement a radiotechnology such as Global System for Mobile Communications (GSM). AnOFDMA system may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the systems and radiotechnologies mentioned above as well as other systems and radiotechnologies. For clarity, certain aspects of the techniques aredescribed below for LTE, and LTE terminology is used in much of thedescription below.

FIG. 1 shows a wireless communication system 100, which may be an LTEsystem or some other wireless system. System 100 may include a number ofevolved Node Bs (eNBs), relay stations, and other system entities thatcan support communication for a number of UEs. An eNB may be a stationthat communicates with the UEs and may also be referred to as a basestation, a Node B, an access point, etc. An eNB may providecommunication coverage for a particular geographic area. In 3GPP, theterm “cell” can refer to a coverage area of an eNB and/or an eNBsubsystem serving this coverage area, depending on the context in whichthe term is used. An eNB may support one or multiple (e.g., three)cells.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG)). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a pico cell may be referred to asa pico eNB. An eNB for a femto cell may be referred to as a femto eNB ora home eNB. In FIG. 1, an eNB 110 may be a macro eNB for a macro cell102, an eNB 114 may be a pico eNB for a pico cell 104, and an eNB 116may be a femto eNB for a femto cell 106. A system controller 140 maycouple to a set of eNBs and may provide coordination and control forthese eNBs.

A relay station 120 may be a station that receives a transmission ofdata and/or other information from an upstream station (e.g., eNB 110 orUE 130) and sends a transmission of the data and/or other information toa downstream station (e.g., UE 130 or eNB 110). A relay station may alsobe referred to as a relay, a relay eNB, etc. A relay station may also bea UE that relays transmissions for other UEs. In FIG. 1, relay station120 may communicate with eNB 110 and UE 130 in order to facilitatecommunication between eNB 110 and UE 130.

UEs 130, 132, 134 and 136 may be dispersed throughout the system, andeach UE may be stationary or mobile. A UE may also be referred to as aterminal, a mobile station, a subscriber unit, a station, etc. A UE maybe a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, etc. AUE may communicate with eNBs and/or relay stations on the downlink anduplink. The downlink (or forward link) refers to the communication linkfrom an eNB to a relay station or from an eNB or a relay station to aUE. The uplink (or reverse link) refers to the communication link fromthe UE to the eNB or relay station or from the relay station to the eNB.In FIG. 1, UE 132 may communicate with eNB 110 via a downlink 122 and anuplink 124. UE 130 may communicate with relay station 120 via an accessdownlink 152 and an access uplink 154. Relay station 120 may communicatewith eNB 110 via a backhaul downlink 142 and a backhaul uplink 144.

In general, an eNB may communicate with any number of UEs and any numberof relay stations. Similarly, a relay station may communicate with anynumber of eNBs and any number of UEs. For simplicity, much of thedescription below is for communication between eNB 110 and UE 130 viarelay station 120.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition a frequency range into multiple(N_(FFT)) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (N_(FFT))may be dependent on the system bandwidth. For example, N_(FFT) may beequal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5,5, 10 or 20 megahertz (MHz), respectively.

The system may utilize FDD or TDD. For FDD, the downlink and uplink areallocated separate frequency channels. Downlink transmissions and uplinktransmissions may be sent concurrently on the two frequency channels.For TDD, the downlink and uplink share the same frequency channel.Downlink and uplink transmissions may be sent on the same frequencychannel in different time intervals.

FIG. 2 shows a frame structure 200 used for FDD in LTE. The transmissiontimeline for each of the downlink and uplink may be partitioned intounits of radio frames. Each radio frame may have a predeterminedduration (e.g., 10 milliseconds (ms)) and may be partitioned into 10subframes with indices of 0 through 9. Each subframe may include twoslots. Each radio frame may thus include 20 slots with indices of 0through 19. Each slot may include L symbol periods, e.g., L=7 symbolperiods for a normal cyclic prefix (as shown in FIG. 2) or L=6 symbolperiods for an extended cyclic prefix. The 2L symbol periods in eachsubframe may be assigned indices of 0 through 2L−1. On the downlink, anOFDM symbol may be sent in each symbol period of a subframe. On theuplink, an SC-FDMA symbol may be sent in each symbol period of asubframe.

On the downlink in LTE, eNB 110 may transmit a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS) in the center1.08 MHz of the system bandwidth for each cell in the eNB. The PSS andSSS may be sent in symbol periods 6 and 5, respectively, in subframes 0and 5 of each radio frame with the normal cyclic prefix, as shown inFIG. 2. The PSS and SSS may be used by UEs for cell search andacquisition. eNB 110 may transmit a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0 in certain radio frames.The PBCH may carry some system information.

eNB 110 may transmit a Physical Control Format Indicator Channel(PCFICH) in the first symbol period of each subframe, as shown in FIG.2. The PCFICH may convey the number of symbol periods (M) used forcontrol channels in a subframe, where M may be equal to 1, 2, 3 or 4 andmay change from subframe to subframe. eNB 110 may transmit a PhysicalHARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel(PDCCH) in the first M symbol periods of each subframe (not shown inFIG. 2). The PHICH may carry information to support HARQ. The PDCCH maycarry information for resource allocation for UEs and controlinformation for downlink channels. The first M OFDM symbols of thesubframe may be referred to as TDM control symbols. A TDM control symbolmay be an OFDM symbol carrying control information. eNB 110 may transmita Physical Downlink Shared Channel (PDSCH) in the remaining symbolperiods of each subframe. The PDSCH may carry data for UEs scheduled fordata transmission on the downlink.

FIG. 3 shows a frame structure 300 used for TDD in LTE. LTE supports anumber of downlink-uplink configurations for TDD. Subframes 0 and 5 areused for the downlink (DL) and subframe 2 is used for the uplink (UL)for all downlink-uplink configurations. Subframes 3, 4, 7, 8 and 9 mayeach be used for the downlink or uplink depending on the downlink-uplinkconfiguration. Subframe 1 includes three special fields composed of aDownlink Pilot Time Slot (DwPTS) used for downlink control channels aswell as data transmissions, a Guard Period (GP) of no transmission, andan Uplink Pilot Time Slot (UpPTS) used for either a random accesschannel (RACH) or sounding reference signals (SRS). Subframe 6 mayinclude only the DwPTS, or all three special fields, or a downlinksubframe depending on the downlink-uplink configuration. The DwPTS, GPand UpPTS may have different durations for different subframeconfigurations.

On the downlink, eNB 110 may transmit the PSS in symbol period 2 ofsubframes 1 and 6, the SSS in the last symbol period of subframes 0 and5, and the PBCH in subframe 0 of certain radio frames. eNB 110 may alsotransmit the PCFICH, PHICH, PDCCH and PDSCH in each downlink subframe.

The various signals and channels in LTE are described in 3GPP TS 36.211,entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation,” which is publicly available. Frame structures200 and 300 are also described in 3GPP TS 36.211.

LTE supports transmission of unicast information to specific UEs. LTEalso supports transmission of broadcast information to all UEs andmulticast information to groups of UEs. A multicast/broadcasttransmission may also be referred to as an MBSFN transmission. Asubframe used for sending unicast information may be referred to as aregular subframe. A subframe used for sending multicast and/or broadcastinformation may be referred to as an MBSFN subframe.

FIG. 4 shows two exemplary regular subframe formats 410 and 420 for thenormal cyclic prefix. The available time frequency resources may bepartitioned into resource blocks. Each resource block may cover 12subcarriers in one slot and may include a number of resource elements.Each resource element may cover one subcarrier in one symbol period andmay be used to send one modulation symbol, which may be a real orcomplex value.

Subframe format 410 may be used by an eNB equipped with two antennas. Acell-specific reference signal may be sent in symbol periods 0, 4, 7 and11 and may be used by UEs for channel estimation and measurement ofchannel conditions or quality. A reference signal is a signal that isknown a priori by a transmitter and a receiver and may also be referredto as pilot. A cell-specific reference signal is a reference signal thatis specific for a cell, e.g., generated with one or more symbolsequences determined based on a cell identity (ID). For simplicity, acell-specific reference signal may be referred to as simply a referencesignal. In FIG. 4, for a given resource element with label R_(a), areference symbol may be sent on that resource element from antenna a,and no modulation symbols may be sent on that resource element fromother antennas. Subframe format 420 may be used by an eNB equipped withfour antennas. A reference signal may be sent in symbol periods 0, 1, 4,7, 8 and 11.

In the example shown in FIG. 4, three TDM control symbols are sent in aregular subframe with M=3. The PCFICH may be sent in symbol period 0,and the PDCCH and PHICH may be sent in symbol periods 0 to 2. The PDSCHmay be sent in the remaining symbol periods 3 to 13 of the subframe.

FIG. 5 shows two exemplary MBSFN subframe formats 510 and 520 for thenormal cyclic prefix. Subframe format 510 may be used by an eNB equippedwith two antennas. A reference signal may be sent in symbol period 0.For the example shown in FIG. 5, M=1 and one TDM control symbol is sentin the MBSFN subframe. Subframe format 520 may be used by an eNBequipped with four antennas. A reference signal may be sent in symbolperiods 0 and 1. For the example shown in FIG. 5, M=2 and two TDMcontrol symbols are sent in the MBSFN subframe.

In general, the PCFICH may be sent in symbol period 0 of an MBSFNsubframe, and the PDCCH and PHICH may be sent in symbol periods 0 toM−1. Broadcast/multicast information may be sent in symbol periods Mthrough 13 of the MBSFN subframe. Alternatively, no transmissions may besent in symbol periods M through 13. An eNB may transmit MBSFN subframeswith a periodicity of 10 ms, e.g., in subframe t of every radio frame.The eNB may broadcast system information indicating which subframes areMBSFN subframes.

In general, an MBSFN subframe is a subframe that carries a limitedreference signal and limited control information in a control portion ofthe subframe and may or may not carry multicast/broadcast data in a dataportion of the subframe. A station (e.g., an eNB or a relay station) maydeclare a subframe as an MBSFN subframe (e.g., via system information)to UEs. These UEs may then expect the reference signal and controlinformation in the control portion of the MBSFN subframe. The stationmay separately inform a UE (e.g., via upper layer signaling) to expectbroadcast data in the data portion of the MBSFN subframe, and the UEwould then expect broadcast data in the data portion. The station mayelect to not inform any UE to expect broadcast data in the data portionof the MBSFN subframe, and the UEs would not expect broadcast data inthe data portion. These characteristics of the MBSFN subframe may beexploited to support relay operation, as described below.

FIGS. 4 and 5 show some subframe formats that may be used for thedownlink. Other subframe formats may also be used, e.g., for more thantwo antennas.

FIG. 6 shows an exemplary interlace structure 600. For FDD, interlacestructure 600 may be used for each of the downlink and uplink. For TDD,interlace structure 600 may be used for both the downlink and uplink. Asshown in FIG. 6, S interlaces with indices of 0 through S−1 may bedefined, where S may be equal to 6, 8, 10, or some other value. Eachinterlace may include subframes that are spaced apart by S frames. Inparticular, interlace s may include subframes s, s+S, s+2S, etc., wheresε{0, . . . , S−1}. The interlaces may also be referred to as HARQinterlaces.

The system may support HARQ for data transmission on the downlink anduplink. For HARQ, a transmitter may send one or more transmissions of apacket until the packet is decoded correctly by a receiver or some othertermination condition is encountered. A modulation and coding scheme(MCS) may be selected for the packet such that it can be decodedcorrectly after a particular number of transmissions, which may bereferred to as a target termination. For synchronous HARQ, alltransmissions of the packet may be sent in subframes of a singleinterlace. For asynchronous HARQ, each transmission of the packet may bescheduled and sent in any subframe.

FIG. 7A shows data transmission on the downlink with HARQ via relaystation 120. eNB 110 may have data to send to UE 130 and may schedule UE130 for data transmission on the downlink. eNB 110 may send a downlink(DL) grant and data on the backhaul link in subframe t₁. The downlinkgrant may indicate the assigned resources, the selected modulation andcoding scheme (MCS), etc. Relay station 120 may receive the downlinkgrant and data transmission from eNB 110 and may process the datatransmission in accordance with the downlink grant. Depending on thedecoding result, relay station 120 may send an acknowledgement (ACK) ora negative acknowledgement (NAK) in subframe t₁+Q, where Q is the delayfor an HARQ response. eNB 110 may retransmit the data in subframe t₁+Sif a NAK is received and may transmit new data if an ACK is received,where S is the number of subframes in an interlace. Data transmission byeNB 110 and ACK/NAK feedback by relay station 120 for the backhaul linkmay continue in similar manner.

For the access link, relay station 120 may send the downlink grant anddata in subframe t₂, which may be offset from subframe t₁ by a suitableamount. For example, subframe t₂ may be a subframe in which relaystation 120 has successfully decoded the data intended for UE 130 fromeNB 110. UE 130 may receive the downlink grant and data transmissionfrom relay station 120, process the data transmission in accordance withthe downlink grant, and send an ACK or a NAK in subframe t₂+Q. Relaystation 120 may retransmit the data in subframe t₂+S if a NAK isreceived and may transmit new data if an ACK is received. Datatransmission by relay station 120 and ACK/NAK feedback by UE 130 for theaccess link may continue in similar manner.

FIG. 7B shows data transmission on the uplink with HARQ via relaystation 120. UE 130 may have data to send on the uplink and may send aresource request in subframe t₃. Relay station 120 may receive theresources request, schedule UE 130 for data transmission on the uplink,and send an uplink (UL) grant in subframe t₃+Q. UE 130 may send a datatransmission in accordance with the uplink grant in subframe t₃+S. Relaystation 120 may process the data transmission from UE 130 and may sendan ACK or a NAK in subframe t₃+Q+S depending on the decoding result. UE130 may retransmit the data in subframe t₃+2S if a NAK is received andmay transmit new data if an ACK is received. Data transmission by UE 130and ACK/NAK feedback by relay station 120 for the access link maycontinue in similar manner.

For the backhaul link, relay station 120 may send a resource request insubframe t₄. eNB 110 may receive the resources request, schedule relaystation 120 for data transmission on the uplink, and send an uplinkgrant in subframe t₄+Q. Relay station 120 may send a data transmissionin accordance with the uplink grant in subframe t₄+S. eNB 110 mayprocess the data transmission from relay station 120 and may send an ACKor a NAK in subframe t₄+Q+S. Relay station 120 may retransmit the dataor transmit new data in subframe t₄+2S depending on whether ACK or NAKwas received. Data transmission by relay station 120 and ACK/NAKfeedback by eNB 110 for the backhaul link may continue in similarmanner.

FIGS. 7A and 7B show synchronous HARQ in which data may be sent inevenly spaced subframes, and ACK information may be sent at a fixedoffset Q from the subframes used to send data. For FDD in LTE, S may beequal to 8, and Q may be equal to 4. Data may be sent in subframes inone interlace, which may be spaced apart by 8 subframes. For TDD in LTE,S may be equal to 10, and Q may be variable and dependent on theselected downlink-uplink configuration. S and Q may also have othervalues. For asynchronous HARQ, data may be sent in any subframe, and ACKinformation may be sent at a fixed or variable offset from the subframeused to send data. S and Q may be different for different transmissionsof data with asynchronous HARQ and also with TDD.

A number of HARQ processes may be defined for each link. An HARQ processmay carry all transmissions of a packet on a given interlace until thepacket is decoded correctly and may then carry transmissions of anotherpacket. A new packet may be sent on an HARQ process when that processbecomes available.

1. Use of Blank Subframes or 8 ms MBSFN Subframes

Relay station 120 typically cannot transmit and receive on the samefrequency channel at the same time. Hence, some of the availablesubframes may be allocated for the backhaul link and may be referred toas backhaul subframes. The remaining subframes may be allocated for theaccess link and may be referred to as access subframes. Relay station120 may communicate with eNB 110 in the backhaul subframes and maycommunicate with UE 130 in the access subframes.

In an aspect, relay station 120 may configure the backhaul subframes asblank subframes on the access link. In one design, a blank subframe mayinclude no transmissions, i.e., no reference signal, no controlinformation, and no data. Relay station 120 may transmit nothing in eachblank subframe in order to be able to listen to eNB 110 on the backhauldownlink. Relay station 120 may transmit the blank subframes with aperiodicity of S subframes to match the periodicity of data sent withHARQ. In one design, S may be equal to 8 subframes (or 8 ms) for FDD ormay be equal to 10 subframes (or 10 ms) for TDD. eNB 110 may alsoconfigure the access subframes as blank subframes. eNB 110 may transmitnothing in each blank subframe in order to avoid causing interference onthe downlink. UE 130 may then observe less interference from eNB 110during the blank subframes of eNB 110.

Blank subframes may be used to support relay operation. Blank subframesmay also be used for other purposes such as interference management forrange extension and restricted association. Range extension is ascenario in which a UE connects to an eNB with lower pathloss among alleNBs detected by the UE. This may lead to a situation in which the UEconnects to an eNB with weaker signal than some other eNBs. For example,in FIG. 1, UE 134 may connect to pico eNB 114 with lower pathloss andlower received signal quality and may observe high interference frommacro eNB 110. For range extension, macro eNB 110 may reserve a set ofsubframes that may be used by pico eNB 114 to send data to UE 134. MacroeNB 110 may configure the reserved subframes as blank subframes. PicoeNB 114 may also declare the subframes used by macro eNB 110 as blanksubframes so that UE 134 will not measure high interference from macroeNB 110.

Restricted association is a scenario in which a UE may be close to afemto eNB but may be unable to access the femto eNB (e.g., due to thefemto eNB belonging to another user). The UE may then connect to anothereNB with lower received power. For example, in FIG. 1, UE 136 may closeto femto eNB 116 but may be unable to access femto eNB 116. UE 136 maythen connect to macro eNB 110 and may observe high interference fromfemto eNB 116. Femto eNB 116 may transmit some blank subframes to avoidcausing interference to UE 136. UE 136 may then communicate with macroeNB 110 in the blank subframes.

Blank subframes may also be used to transmit new control channels tosupport technologies such as network multiple-input multiple-output(MIMO), higher order MIMO, etc. Network MIMO refers to transmission frommultiple cells to one or multiple UEs. For network MIMO, some subframesmay be advertised as blank subframes to legacy UEs and would not be usedby the legacy UEs for channel estimation, interference estimation,measurements, or other purposes. Transmissions for network MIMO may besent in these subframes and would not impact the legacy UEs.

LTE currently supports MBSFN subframes with a periodicity of 10 ms forFDD. LTE also currently supports synchronous HARQ with a periodicity of8 ms. The MBSFN subframes may not be aligned with subframes used fordata transmission. For example, MBSFN subframes may be declared forsubframes 0, 10, 20, etc., and data may be sent with HARQ in subframes0, 8, 16, etc.

In another aspect, MBSFN subframes with a periodicity of 8 ms may besupported for FDD to match the periodicity of data sent with HARQ. TheLTE standard may be changed to support 8 ms MBSFN subframes and/or othersuitable value of S to match the periodicity of data.

Relay station 120 may use some interlaces for the backhaul link and mayuse the remaining interlaces for the access link. The subframes in theinterlaces for the backhaul link may be declared as MBSFN subframes. Insome cases, relay station 120 may deviate from the normal partitioning.For example, relay station 120 may transmit the PSS, SSS, and PBCH incertain subframes (e.g., subframes 0 and 5 in FDD) that may be part ofthe interlaces allocated to the backhaul link. Relay station 120 may useregular subframes instead of MBSFN subframes for these subframes. In onedesign, relay station 120 may transmit only the PSS and SSS in theregular subframes used for subframes 0 and 5. In another design, relaystation 120 may transmit the TDM control symbols as well as the PSS andSSS in the regular subframes used for subframes 0 and 5.

In another aspect, a bitmap may be used to convey different types ofsubframes used by relay station 120 or eNB 110. In general, the bitmapmay cover any duration, e.g., any number of radio frames. The bitmap mayindicate the type of each subframe covered by the bitmap.

FIG. 8 shows a design of a bitmap 800 for R radio frames i throughi+R−1, where R may be equal to 2, 4, etc. The bitmap may include one bitfor each subframe covered by the bitmap. The bit for each subframe maybe set to a first value (e.g., ‘0’) to indicate a regular subframe or toa second value (e.g., ‘1’) to indicate an MBSFN subframe. The secondvalue may also indicate a blank subframe if it is used instead of anMBSFN subframe. The bitmap can flexibly allow each subframe to be set toone of the supported subframe types. In one design, the bitmap may coverfour radio frames and may include 40 bits for 40 subframes. The bitmapmay be sent via a broadcast channel (e.g., the PBCH) or some otherchannel.

In another design, subframes may be allocated in units of interlaces.The interlace(s) with subframes designated as MBSFN subframes (or asblank subframes) may be conveyed via the broadcast channel. Thesubframes designated as MBSFN subframes (or as blank subframes) may alsobe conveyed in other manners.

The blank subframes and/or MBSFN subframes may be conveyed to UEs viasignaling, e.g., a bitmap. The UEs may be aware of the blank subframesand/or MBSFN subframes. The UEs may not expect reference signals in theblank subframes and may expect limited reference signals in the MBSFNsubframes. The UEs may not use the blank subframes for (intra-frequencyand inter-frequency) measurement, channel estimation, and interferenceestimation. The UEs may perform measurement, channel estimation, andinterference estimation based on regular subframes. The UEs may or maynot use the MBSFN subframes for measurement, channel estimation, andinterference estimation. The UEs may perform channel estimation based onthe reference signals in the regular subframes and possibly the MBSFNsubframes.

The UEs may perform interference estimation based on an appropriateportion of the regular subframes and possibly the MBSFN subframes.Interference may vary (i) across an MBSFN subframe due to the TDMstructure of TDM control symbols within the MBSFN subframe and (ii)between MBSFN subframes and other subframes due to the TDM structure ofthe MBSFN subframes. The UEs may perform interference estimation bytaking into account the variation in interference. For example, if a UEknows that OFDM symbol 0 has higher interference than other OFDMsymbols, then the UE may estimate interference separately for OFDMsymbol 0 and the other OFDM symbols. The UE may perform interferenceestimation based on the reference signal. The UE may obtain aninterference estimate for OFDM symbol 0 using only the reference signalin OFDM symbol 0. The UE may obtain an interference estimate for theother OFDM symbols using the reference signal sent in these OFDMsymbols.

2. MBSFN Subframes & Time Offset

eNB 110 may transmit TDM control symbols in the first M symbol periodsof each subframe. Relay station 120 may also transmit TDM controlsymbols in the first M symbol periods of each subframe. Relay station120 may not be able to simultaneously receive the TDM control symbolsfrom eNB 110 and transmit its TDM control symbols to its UEs.

In another aspect, the timing of relay station 120 may be offset by Nsymbol periods from the timing of eNB 110, where N may be any suitablevalue. The timing offset may be selected such that the TDM controlsymbols and/or the reference signal of relay station 120 do not overlapwith those of eNB 110.

FIG. 9 shows a design of symbol timing offset between eNB 110 and relaystation 120. In general, the timing of relay station 120 may be advanced(as shown in FIG. 9) or delayed by N symbol periods relative to thetiming of eNB 110. The timing offset may enable relay station 120 toreceive the TDM control symbols from eNB 110.

eNB 110 may transmit the reference signal (RS) and data to relay station120 in subframe t of eNB 110. Relay station 120 may behave as a UE insubframe q of relay station 120 and may not transmit the referencesignal, control information, and/or data to its UEs. Relay station 120may configure its subframe q as an MBSFN subframe and may transmit oneor more TDM control symbols in subframe q. This may reduce the number ofsymbols in which relay station 120 needs to transmit reference to itsUEs and may allow relay station 120 to listen to more symbolstransmitted by eNB 110 in subframe t. The MBSFN subframe may allow forselection of more efficient timing offset between relay station 120 andeNB 110.

As shown in FIG. 9, relay station 120 may receive only the first 14−NOFDM symbols from eNB 110 in subframe t since it may transmit its TDMcontrol symbol(s), reference signal, and/or data during the last N OFDMsymbols in subframe t (which corresponds to subframe q+1 of relaystation 120). Relay station 120 may transmit a single TDM control symbolwith MBSFN subframe format 510 in FIG. 5, and N may be equal to one. Inone design, on the downlink, eNB 110 may send data and reference signalto relay station 120 within the first 14−N OFDM symbols of subframe t.An interleaving scheme may interleave data sent to relay station 120across the first 14−N OFDM symbols (instead of all 14 OFDM symbols).Similarly, on the uplink, relay station 120 may send data to eNB 110 in14−N OFDM symbols (instead of all 14 OFDM symbols). An interleavingscheme may spread the data sent by relay station 120 over 14−N OFDMsymbols. For both the downlink and uplink, interleaving over 14−N OFDMsymbols with a timing offset of N symbol periods may improve dataperformance.

In one design, consecutive subframes may be used for communicationbetween eNB 110 and relay station 120. This may result in N OFDM symbolsbeing lost in only one subframe instead of in each subframe. Forexample, if relay station 120 marks K consecutive subframes as blanksubframes and has an timing advance of N symbols, then there are K−1subframes of eNB 110 during which relay station 120 does not transmitany reference signals, control information, or data and may then be ableto listen to eNB 110 in all symbol periods. In the subframe followingthese K−1 subframes, relay station 120 may transmit in the last N OFDMsymbols and hence may be able to listen to only 14−N symbols. If relaystation 120 marks the K subframes as MBSFN subframes instead of blanksubframes and transmits on only one TDM control symbol in each MBSFNsubframe, then it may lose N OFDM symbols in the last subframe and oneOFDM symbol in the other K−1 subframes.

If MBSFN subframes with periodicity of 8 ms are supported, then eNB 110may transmit in accordance with 8 ms HARQ timeline to relay station 120.Relay station 120 may declare MBSFN subframes for subframes in which eNB110 transmits to relay station 120. If MBSFN subframes with periodicityof 10 ms are supported, then eNB 110 may transmit in accordance with 10ms HARQ timeline to relay station 120. eNB 110 may then ensure thatresources (e.g., for downlink and uplink control, data, etc.) for 8 msUEs and 10 ms relay stations do not collide. For uplink controlresources, eNB 110 may use different offsets for demodulation referencesignals (DMRS) from relay stations and UEs. Alternately, the relaystations and UEs may be frequency division multiplexed (FDM).

MBSFN subframes or blank subframes and time offset may be used tosupport relay operation, as described above. MBSFN subframes or blanksubframes and time offset may also be used for interference management,e.g., for range extension and restricted association.

3. MBSFN Subframes & New Control Channels

In another aspect, eNB 110 may transmit new control channels, referencesignal, and data to relay station 120 during the time that relay station120 is not transmitting. This may then allow relay station 120 toreceive the control channels. Relay station 120 may configure suchsubframes as MBSFN subframes so that it can transmit only the TDMcontrol symbols and can use the remaining symbols to listen to eNB 110.

FIG. 10 shows a design of downlink transmissions by eNB 110 with newcontrol channels. eNB 110 may transmit to relay station 120 in subframet and to its UEs in subframe t+1. Relay station 120 may receive from eNB110 in subframe t (which may correspond to subframe q of relay station120) and may transmit to its UEs in subframe t+1 (which may correspondto subframe q+1 of relay station 120). The timing of relay station 120may be aligned with the timing of eNB 110.

In the design shown in FIG. 10, eNB 110 may or may not transmit TDMcontrol symbols in the first M symbol periods of subframe t. eNB 110 maytransmit new control channels as well as data in the remaining symbolperiods of subframe t to relay station 120. A default value (e.g., M=3)may be assumed for the PCFICH, or the PCFICH may be sent as one of thecontrol channels. eNB 110 may also transmit a reference signal (RS)using the format for a regular subframe (e.g., as shown in FIG. 4) or anew format. eNB 110 may also serve other UEs and/or other relay stationsin subframe t. Relay station 120 may transmit its TDM control symbols inthe first M symbol periods of subframe t, e.g., using an MBSFN subframeformat. Relay station 120 may then switch to receive the transmissionsfrom eNB 110 in the remaining symbol periods of subframe t.

eNB 110 may transmit to relay station 120 in subframes that relaystation 120 is mandated to transmit. For example, eNB 110 may transmitin subframes 0 and 5 of relay station 120, which may transmit the PSSand SSS. eNB 110 may then transmit the control channels and data torelay station 120 in OFDM symbols in which relay station 120 is nottransmitting. eNB 110 may be aware of mandated transmissions by relaystation 120 and can thus avoid transmitting to relay station 120 duringthese mandated transmissions.

MBSFN subframes and new control channels may also be used forinterference management (e.g., for range extension and restrictedassociation) and to support technologies such as network MIMO. Forexample, a dominant interferer may configure a few subframes as MBSFNsubframes. In these subframes, a weaker eNB can communicate with its UEsin symbol periods not used by the dominant interferer.

4. Mechanisms for Dealing with Subframes 0 and 5

Relay station 120 may have various restrictions that may impact itsoperation. For example, relay station 120 may communicate with eNB 110via the backhaul downlink and uplink and may also communicate with UE130 via the access downlink and uplink, as shown in FIG. 1. Since relaystation 120 typically cannot transmit and receive on the same frequencychannel at the same time, the backhaul link and the access link may betime division multiplexed. Relay station 120 may then be able tocommunicate on only the backhaul link or the access link in eachsubframe.

LTE supports asynchronous HARQ on the downlink and synchronous HARQ onthe uplink. For HARQ, a transmission of data may be sent in subframe tand may be received in error. A retransmission of the data may be sentin any subframe for asynchronous HARQ or in a specific subframe (e.g.,subframe t+8) for synchronous HARQ. Synchronous HARQ may thus restrictwhich subframes can be used for retransmissions.

Relay station 120 may declare backhaul subframes as MBSFN subframes oras blank subframes. This may allow relay station 120 to transmit aminimum amount of control information and reference signal, as shown inFIG. 5. However, the MBSFN subframes may be restricted to a periodicityof 10 ms (if 8 ms MBSFN subframes are not supported, as in LTE Release8). Relay station 120 may be required to transmit the PSS and SSS insubframes 0 and 5. The various restrictions on relay station 120 may beaddressed in several manners.

FIG. 11 shows a design of communication by relay station 120 with a 10ms timeline. In this design, relay station 120 may have some backhaulsubframes in each radio frame for communication with eNB 110 and someaccess subframes in each radio frame for communication with UE 130.Subframes 0 and 5 may be access subframes to allow relay station 120 totransmit the PSS and SSS in these subframes. Relay station 120 maytransmit to and/or receive from eNB 110 in each backhaul subframe. Relaystation 120 may transmit to and/or receive from UE 130 in each accesssubframe. Relay station 120 may declare the backhaul subframes as MBSFNsubframes (as shown in FIG. 11), which may have a periodicity of 10 ms,or as blank subframes.

In the example shown in FIG. 11, subframes 0, 4 and 5 in the downlinkand subframe 4, 8 and 9 in the uplink of each radio frame may be accesssubframes. Subframes 1, 2, 3, 6, 7, 8 and 9 in the downlink andsubframes 0, 1, 2, 3, 5, 6 and 7 in the uplink of each radio frame maybe backhaul subframes. For the access downlink, relay station 120 maytransmit data to UE 130 in subframes 0, 4 and 5 and may receive ACKinformation (e.g., ACK or NAK) from UE 130 in subframes 4, 8 and 9,respectively. Since asynchronous HARQ is used for the downlink, relaystation 120 may send retransmissions in subframes 0, 4 and 5. The accessdownlink may operate with a 10 ms timeline. For example, relay station120 may send a transmission in subframe 0 of a given radio frame,receive NAK in subframe 4, and then send a retransmission in subframe 0of the next radio frame.

For the access uplink, UE 130 may send data to relay station 120 insubframes 4, 8 and 9 and may receive ACK information from relay station120 in subframes 8, 2 and 3, respectively. Relay station 120 may targetthe first transmission for legacy UEs and may operate with a 10 mstimeline for new UEs. In one design, if the first transmission isunsuccessful, then UE 130 may be configured to transmit in othersubframes. Since synchronous HARQ is used for the uplink, UE 130 maysend retransmissions in specific subframes. For example, UE 130 may senda transmission of a packet in subframe 4 of a given radio frame and mayreceive ACK information in subframe 8. Since subframe 8 is an MBSFNsubframe, relay station 120 can send the ACK information on the accessdownlink in this subframe even though it is reserved for the backhauldownlink. UE 130 may receive NAK in subframe 8 and may retransmit thedata in the following subframe 2. However, this uplink subframe may bereserved for the backhaul uplink. In this case, relay station 120 may(i) listen to UE 130 and cancel its uplink transmission or (ii) continuetransmission in the backhaul uplink and ignore the UE retransmissionuntil the retransmission coincide with a subframe for the access uplink.

In another design, an “ACK and suspend” procedure may be used. Forexample, relay station 120 may schedule UE 130 on the uplink with atarget termination of one transmission. UE 130 may send a transmissionof a packet. If relay station 120 is unable to send ACK information forthis transmission (e.g., because relay station 120 may be listening onthe backhaul link), then UE 130 may treat this as an implicit ACK andmay suspend its transmissions. However, UE 130 does not discard thepacket. If relay station 120 decoded the packet in error, then relaystation 120 can subsequently schedule a second transmission of thepacket in a subframe for which it is able to transmit assignments, andthe suspension covered by the implicit ACK may then be revoked. Asimilar scenario may occur when eNB 110 schedules relay station 120 onthe uplink. Relay station 120 may send the packet but may not be able toreceive the ACK information from eNB 110 because it may be transmittingto UE 130 on the access link. Relay station 120 may treat it as animplicit ACK but may not discard the packet. If eNB 110 decoded thepacket in error, then it can schedule relay station 120 to retransmitthe packet on the uplink.

FIG. 12 illustrates selection of a target termination based ontransmission opportunities. FIG. 12 shows a different partition betweenthe access link and the backhaul link than the partition shown in FIG.11. In the example shown in FIG. 12, subframes 0, 2, 4, 5, 6 and 8 inthe downlink and subframes 0, 1, 3, 4 and 8 in the uplink are used forthe access link while the remaining subframes are used for the backhaullink. Relay station 120 may mark the backhaul subframes as blanksubframes and may not transmit any control information or data to itsUEs in these subframes. In one design, UE 130 may send a packet with atarget termination determined based on ACK transmission opportunitiesavailable to relay station 120. An ACK transmission opportunity maycorrespond to a subframe in which ACK information can be sent (due tosynchronous HARQ requirement) and which is available for use. In theexample shown in FIG. 12, UE 130 may start transmission of the packet insubframe 0 of radio frame i and may have a data transmission opportunityin subframe 8 but no data transmission opportunity in subframe 6 of thenext radio frame i+1. Relay station 120 may have ACK transmissionopportunities in subframe 4 of radio frame i as well as subframe 2 ofthe next radio frame. Relay station 120 may then select a targettermination of two transmissions for the packet for UE 130. UE 130 mayalso start transmission of a packet in subframe 1 of radio frame i andmay have a target termination of one transmission due to no datatransmission opportunity in subframe 9, as shown in FIG. 12.

Relay station 120 may send ACK information after each transmission ofdata by UE 130, e.g., as shown by the first two examples in FIG. 12. Inanother design, relay station 120 may not be able to send ACKinformation after each transmission of data and may send the ACKinformation at the next ACK transmission opportunity. For example, UE130 may send a first transmission of a packet in subframe 3 of radioframe i, receive no ACK information in subframe 7, send a secondtransmission of the packet in subframe 1 of the next radio frame i+1,and receive ACK information for the packet in subframe 5 of the nextradio frame, as shown by the third example in FIG. 12. Relay station 120may select a target termination of two transmissions for the packet tomake efficient use of the uplink resources.

In general, the target termination for a packet may be determined basedon the first subframe that cannot be used to send the packet or based onwhen ACK information can be sent and/or received. In one design, ACKinformation may be sent after each transmission of the packet. In thisdesign, the target termination may be selected based on the firstsubframe in which ACK transmission opportunities are not available forthe packet. In another design, ACK information may be delayed. In thisdesign, the target termination for the packet may be K transmissions ifan ACK transmission opportunity is available for the packet after Ktransmissions, where K may be any integer value greater than or equal toone. In the exemplary partition shown in FIG. 12, relay station 120 mayselect (i) a target termination of one transmission for a packet sentstarting in subframe 1, 4 or 8 and (ii) a target termination of twotransmissions for a packet sent starting in subframe 0 or 3.

In another design, UE 130 may send packets to relay station 120 in amanner to target termination of each packet on the first transmission.In this case, relay station 120 would not need to monitor othersubframes for retransmissions. For packets that do not terminate on thefirst transmission, UE 130 may send retransmissions in accordance withsynchronous HARQ. Relay station 120 may receive the retransmissions sentby UE 130 in backhaul subframes instead of listening to eNB 110.Alternatively, relay station 120 may ignore the retransmissions sent byUE 130 in backhaul subframes and may wait for subsequent retransmissionssent in access subframes, which may result in higher latency. Ingeneral, relay station 120 may receive retransmissions from UE 130whenever possible and may ignore retransmissions that cannot be receivedfor whatever reason.

For the example shown in FIG. 12, relay station 120 may communicate witheNB 110 via the backhaul downlink in subframes 1, 3, 7 and 9 and via thebackhaul uplink in subframes 2, 5, 6, 7 and 9 in an analogous manner.For the backhaul downlink, eNB 110 may transmit data to relay station120 in subframes 1 and 3 and may receive ACK information in subframes 5and 7, respectively. eNB 110 may also send retransmissions in anysuitable subframe with asynchronous HARQ. For the backhaul uplink, relaystation 120 may send data to eNB 110 in subframes 5, 7 and 9 and mayreceive ACK information in subframes 9, 1, and 3, respectively. Relaystation 120 may send packets to eNB 110 based on the data transmissionopportunities available to relay station 120 and the ACK transmissionopportunities available to eNB 110. Some subframes may not have ACKtransmission opportunities. The techniques described above, such as theACK and suspend procedure and the termination target selection, may beused for subframes that do not have corresponding ACK transmissionopportunities. Alternatively, relay station 120 may send packets to eNB110 in a manner to target termination of each packet on the firsttransmission. For packets that do not terminate on the firsttermination, relay station 120 may send retransmissions in accordancewith synchronous HARQ. In one design, relay station 120 may sendretransmissions in backhaul subframes and may skip retransmissions inthe access subframes. eNB 110 may then receive the retransmissions sentby relay station 120 in the backhaul subframes. In another design, relaystation 120 may send retransmissions in both backhaul and accesssubframes. In this design, relay station 120 may skip listening to UE130 in the access subframes. In yet another design, relay station 120may use asynchronous HARQ on the uplink and may send the retransmissionon other backhaul subframes that may not be part of the interlace usedfor the first transmission.

For both the backhaul link and the access link, ACK information may besent a fixed number of subframes (e.g., four subframes) after thecorresponding transmission of data. This may limit the number ofsubframes that may be used to send data on the backhaul and accesslinks. In one design, eNB 110 may send ACK information in non-fixedsubframes (e.g., in the next ACK transmit opportunity) to relay station120. For example, relay station 120 may send a transmission of data toeNB 110 in subframe 1 and may receive ACK information for thistransmission in subframe 6 (instead of subframe 5). Similarly, relaystation 120 may send ACK information in non-fixed subframes (e.g., inthe next ACK transmit opportunity) to eNB 110. For example, eNB 110 maysend a transmission of data to relay station 120 in subframe 1 and mayreceive ACK information for this transmission in subframe 6 (instead ofsubframe 5). Thus, the subframes used to send/receive ACK informationto/from relay station 120 may be different than the subframes that wouldbe used if a legacy/Release 8 UE had been scheduled instead of relaystation 120. For both the backhaul downlink and uplink, relay station120 (or eNB 110) may send signaling to convey use of a differentsubframe for sending ACK information. eNB 110 (or relay station 120) maythen receive the ACK information in the indicated subframe.

Relay station 120 may elect to receive data and/or ACK information fromUE 130 in backhaul subframes and may be unable to send data and/or ACKinformation to eNB 110 in these subframes. Relay station 120 mayindicate this to eNB 110 (e.g., via a control channel) so that eNB 110can wait for data and/or ACK information from relay station 120. eNB 110may also infer this through other means. For example, eNB 110 may beaware that relay station 120 may monitor for ACK information from UE 130in subframe 4 and 9 in response to transmissions of data from relaystation 120 to UE 130 in subframes 0 and 5, respectively. Relay station120 may then send data and/or ACK information in other subframes. If eNB110 is aware that relay station 120 will not use resources in thebackhaul subframes reserved for relay station 120, then eNB 110 mayschedule other UEs on these resources in order to more fully utilize theavailable resources.

In another design, transmissions and retransmissions on the backhaullink and the access link may be sent with 8 ms timelines. One or moreinterlaces may be used for the access link, and the subframes in theinterlace(s) may be access subframes. The remaining interlaces may beused for the backhaul link, and the subframes in these interlaces may bebackhaul subframes. Relay station 120 may configure the backhaulsubframes as MBSFN subframes or blank subframe in order to be able tolisten to eNB 110 efficiently. However, in some subframes of thebackhaul interlaces, relay station 120 may be forced to transmitsignals. For example, in subframes 0 and 5, relay station 120 may berequired to transmit the PSS, SSS, etc. Relay station 120 may sendtransmissions in these backhaul subframes to UE 130, there by convertingthese subframes to access subframes.

Only one HARQ process is typically active on a given interlace at anygiven moment. In one design, multiple HARQ processes may be interleavedon the same interlace to provide more processing time. This interleavingof HARQ processes may be applied to both the access link and thebackhaul link. For example, eNB 110 may transmit packet 1 on the firstdownlink HARQ process to relay station 120 in subframe 6. Relay station120 may be forced to transmit to its UEs in subframe 0 of the next radioframe and may not be able to send ACK information to eNB 110. Insubframe 4 of the next radio frame, eNB 110 may transmit a new packet(packet 2) on a second downlink HARQ process instead of retransmittingpacket 1 on the first downlink HARQ process. The interlace may thenalternate between the packets for the first and second downlink HARQprocesses. This may give relay station 120 more time to send the ACKinformation to eNB 110. eNB 110 may retransmit a packet only if a NACKis received, thus improving relay operation.

Relay station 120 may schedule uplink data for its UEs in an uplinksubframe that carries ACK information corresponding to downlinktransmission in subframes that were initially reserved for the backhaullink, even though the uplink subframe is part of an interlace reservedfor the backhaul link. In this case, relay station 120 may monitor fortransmission in the uplink subframe (as well as an uplink ACK fordownlink data). Relay station 120 may send ACK information for a packetonly when the position of the ACK coincides with an access downlinksubframe when the backhaul subframes are marked as blank subframes. Ifthe backhaul subframes are configured as MBSFN subframes, then relaystation 120 may send the ACK information for the uplink transmission.

Relay station 120 may transmit the PSS and SSS in subframes 0 and 5 ofeach radio frame even for the 8 ms timelines. If a given subframe 0 or 5lies on a backhaul interlace, then relay station 120 may skipcommunication with eNB 110 and may transmit to its UEs in the backhaulsubframe, thereby converting this subframe into an access subframe. Inthis case, relay station 120 may not be able to receive from eNB 110during the subframe. If eNB 110 has ACK information to send to relaystation 120 in the subframe, then eNB 110 may delay transmission of theACK information until the next backhaul subframe. Similarly, if relaystation 120 has ACK information to send to eNB 110 in an uplink subframethat is used for the access link, then relay station 120 may delaytransmission of the ACK information until the next backhaul subframe. Inanother design, relay station 120 may skip mandated transmission such asthe PSS and SSS in subframes 0 and 5 that are backhaul subframes and mayinstead communicate with eNB 110.

In one design, an ACK repetition scheme may be used to ensure that UE130 transmits ACK information in subframes that relay station 120monitors. UE 130 may have ACK information to send in a backhaulsubframe. UE 130 may send the ACK information in this subframe with thepossibility that relay station 120 may monitor the access link insteadof communicating with eNB 110 on the backhaul link. Alternatively oradditionally, UE 130 may send the ACK information in the next accesssubframe that relay station 120 will monitor. UE 130 may send ACKinformation for multiple packets in a given subframe, e.g., ACKinformation to be sent in the current subframe as well as ACKinformation to be sent in a prior subframe that is repeated in thecurrent subframe.

5. Subframe Offset/Periodic Control Channels

In another aspect, the timing of relay station 120 may be offset by aninteger number of subframes from the timing of eNB 110. The subframeoffset may allow relay station 120 to transmit the PSS, SSS and PBCH toits UEs and also receive the PSS, SSS and PBCH from eNB 110.

FIG. 13 shows a design of subframe timing offset between eNB 110 andrelay station 120. The timing of relay station 120 may be delayed (asshown in FIG. 13) or advanced by an integer number of subframes (e.g.,by one subframe) relative to the timing of eNB 110. eNB 110 may transmitthe PSS, SSS, and possibly PBCH in its subframes 0 and 5, which maycorrespond to subframes 9 and 4, respectively, of relay station 120.Relay station 120 can receive the PSS, SSS, and possibly PBCH from eNB110. Relay station 120 may transmit the PSS, SSS and PBCH in itssubframes 0 and 5, which may correspond to subframes 1 and 6,respectively, of eNB 110.

As shown in FIG. 13, a subframe offset between eNB 110 and relay station120 may result in eNB subframe 0 being equal to relay subframe k, wherek≠0. The subframe offset may allow relay station 120 to monitor the PSS,SSS and PBCH from eNB 110. The subframe offset may also allow eNB 110 toschedule system information blocks (SIBs) in a subframe in which relaystation 120 will monitors eNB 110. In some situations, a subframe offsetmay not be sufficient to enable relay station 120 to receive the PSS,SSS, PBCH, and/or SIBs (e.g., for TDD operation where subframe offsetmay not be possible). In these situations, the PSS, SSS, PBCH, and/orSIBs, may be sent in a separate channel to allow relay station 120 toreceive them. Alternately, relay station 120 may periodically tune away(e.g., not transmit data to UE 130) and receive such transmissions fromeNB 110.

Relay station 120 may receive periodic control channels from UE 130and/or may transmit periodic control channels to eNB 110. The periodiccontrol channels may carry channel quality indicator (CQI) information,a sounding reference signal (SRS), etc. LTE currently supportsperiodicity of 2, 5, 10, 20 and 40 ms for the periodic control channels.

On the access link, relay station 120 may monitor subframes with aperiodicity of 8 ms. The periodic control channels may be sent with aperiodicity of 2 ms in order to ensure that relay station 120 canreceive these control channels every 8 ms. Alternately, UE 130 may sendthe periodic control channels with a periodicity of 5, ms or some otherduration. Relay station 120 may either monitor the periodic controlchannels from UE 130 or wait until the periodic control channelscoincide with an access subframe.

In another design, a periodicity of 8 ms, or some other integer multipleof the periodicity of data sent with HARQ, may be supported for theperiodic control channels. This may allow relay station 120 to receiveeach transmission of the periodic control channels sent by UE 130, whichmay avoid wasted UE transmissions. This may also allow eNB 110 toreceive each transmission of the periodic control channels sent by relaystation 120.

6. Asymmetric Backhaul/Access Partition

In another aspect, asymmetric downlink/uplink partitioning of thebackhaul link and the access link may be employed to enable efficientuse of resources. The partitioning may be based on a pattern that mayrepeat every S subframes, where S may be equal to 8, 10, etc. For thedownlink, the S subframes may be partitioned such that U_(DL) subframesare used for the backhaul downlink and V_(DL) subframes are used for theaccess downlink, where S=U_(DL)+V_(DL). For the uplink, the S subframesmay be partitioned such that U_(UL) subframes are used for the backhauluplink and V_(UL) subframes are used for the access uplink, whereS=U_(UL)+V_(UL). For asymmetric downlink/uplink partition, U_(DL)=U_(UL)and V_(DL)≠V_(UL).

FIG. 14 shows an example of asymmetric downlink/uplink partition. Inthis example, S is equal to 8, a 5:3 backhaul/access partition is usedfor the downlink, and a 4:4 backhaul/access partition is used for theuplink. For simplicity, FIG. 14 shows relay station 120 (i) receivingfrom eNB 110 on the backhaul downlink in subframes 0 to 4 and (ii)transmitting to UE 130 on the access downlink in subframes 5 to 7 forthe 5:3 backhaul/access downlink partition. FIG. 14 also shows relaystation 120 (i) transmitting to eNB 110 on the backhaul uplink insubframes 0 to 3 and (ii) receiving from UE 130 on the access uplink insubframes 5 to 7 for the 4:4 backhaul/access uplink partition. As shownin FIG. 14, relay station 120 may transmit and receive on differentfrequency channels in each subframe except for subframe 4, and mayreceive on two frequency channels in subframe 4. Relay station 120 maythus conform to a requirement of not transmitting and receiving on thesame frequency channel at the same time. In general, the subframes usedfor the backhaul and access downlinks may be distributed across the 8subframes, and the subframes used for the backhaul and access uplinksmay also be distributed across the 8 subframes, subject to thetransmit/receive requirement described above.

The backhaul/access partitions for the downlink and uplink may bedetermined in various manners. In one design, the backhaul/accesspartition for each link may be determined based on channel conditions.For example, more subframes may be used for the link with worse channelconditions in order to satisfy data requirements for that link.Alternatively, more subframes may be used for the link with betterchannel conditions in order to improve throughput. In another design,the backhaul/access partition for each link may be dependent on datarequirements for that link, which may in turn be dependent on the numberof UEs being served and the data requirements of each UE. For example,eNB 110 may serve many UEs whereas relay station 120 may serve one orfew UEs. In this case, more subframes may be used for the backhauldownlink and uplink, and fewer subframes may be used for the accessdownlink and uplink. In general, any backhaul/access partition may besupported for the downlink and uplink. Furthermore, MBSFN subframes maybe used to support any backhaul/access partition for each link. MBSFNsubframes may reduce the amount of transmissions by relay station 120and may make it more efficient to listen to eNB 110 in the backhauldownlink subframes. MBSFN subframes that are reserved for the backhaullink may also support transmission of control information to relay UEs.Hence, for the access link, the impact on scheduling uplinktransmissions and sending ACK information for uplink transmissions maybe small. MBSFN subframes may allow efficient operation of relay station120 even with asymmetric partitioning of uplink and downlink subframes.

In one design that is shown in FIG. 14, asymmetric backhaul/accesspartition may be achieved by allocating different numbers of interlacesfor different links. In another design, asymmetric backhaul/accesspartition may be achieved by subsampling of interlaces. For example,even numbered subframes in a given interlace may be used for thebackhaul link, and odd numbered subframes in the interlace may be usedfor the access link. Relay station 120 may know that only alternatesubframes in the interlace are available for the access link and may beable to receive transmissions from UE 130 in these alternate subframes.Relay station 120 may select the modulation and coding scheme for UE 130accordingly. For example, relay station 120 may target termination afterthe first transmission from UE 130.

Due to the asymmetric partitioning, to schedule UE 130 on the accesslink and/or to send ACK information corresponding to an uplinktransmission, relay station 120 may transmit control information insubframes reserved for the backhaul link. If relay station 120 usesMBSFN subframes for the backhaul link, then relay station 120 may beable to send ACK information for data transmission received from UE 130and other control information such as uplink grant in any subframe. Inthis case, relay station 120 may transmit control information andreference signal in the first one or two OFDM symbols of a backhauldownlink subframe marked as an MBSFN subframe by relay station 120 andmay use the remaining symbol periods in the subframe to listen to eNB110. New control channels for uplink and/or downlink may also be used tosend ACK information, grants, and/or other information to/from UEscapable of receiving/transmitting these control channels.

In the backhaul link, for uplink and/or downlink, new control channelsmay be used to send ACK information, grants, etc. The new controlchannels may be sent in a designated subframe (e.g., ACK information maybe sent in subframe t+4 for data transmission sent in subframe t) or ina different subframe. For the 5:3 backhaul/access downlink partitionshown in FIG. 14, the ACK information for the extra backhaul downlinksubframe 4 may be sent in one of the four backhaul uplink subframes.

7. TDD Relay

LTE supports a number of downlink-uplink configurations for TDD. Table 1lists the downlink-uplink configurations supported by LTE Release 8 andprovides the allocation of subframes for each configuration. In Table 1,“D” denotes a downlink subframe, “U” denotes an uplink subframe, and “S”denotes a special subframe comprising the DwPTS, GP and UpPTS fieldsshown in FIG. 3.

TABLE 1 Downlink-Uplink Configurations for TDD Downlink- Uplink Switch-Con- Point Subframe Number figuration Periodicity 0 1 2 3 4 5 6 7 8 9 05 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D SU D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D

A particular downlink-uplink configuration may be selected for use. Theavailable downlink and uplink subframes in the selected downlink-uplinkconfiguration may be allocated to the backhaul link and the access link,which may be time division multiplexed. In one design, blank subframesmay be declared for the backhaul subframes so that UEs served by relaystation 120 can be inactive in these subframes. In another design, MBSFNsubframes may be used for the backhaul subframes.

Relay station 120 may transmit the PSS, SSS, and possibly PBCH insubframes 0, 1, 5 and 6. Relay station 120 may avoid transmitting on theaccess downlink during the backhaul uplink subframes in order to avoidcausing high interference to eNB 110. Relay station 120 may transmit onthe access downlink in the backhaul uplink subframes if it will notcause high interference to eNB 110, e.g., if the downlink antenna beampattern for relay station 120 can provide sufficient RF isolation toavoid jamming eNB 110. Relay station 120 may also schedule uplinktransmissions for its UEs only in subframes that are used by eNB 110 foruplink so that its UEs can avoid causing interference to UEstransmitting to eNB 110.

Table 2 shows some backhaul-access configurations that satisfy theconstraints described above and may be selected for use. In Table 2,backhaul-access configuration X or XY is based on downlink-uplinkconfiguration X. Y denotes one of multiple alternatives (if available)for configuration X. For each backhaul-access configuration in Table 2,subframes allocated for the backhaul link are shown with shading, andsubframes allocated for the access link are shown without shading.

TABLE 2 Backhaul-Access Configurations for TDD

Table 3 lists the number of subframes for each link for eachbackhaul-access configuration in Table 2.

TABLE 3 Number of Subframes for Each Link for TDD Backhaul- Access Con-Backhaul Link Access Link figuration Downlink Uplink Downlink Uplink 1A2 2 4 2 1B 1 1 5 3 1C 1 1 5 3 2A 2 1 6 1 2B 2 1 6 1 3 2 1 5 2 4 3 1 5 1

FIG. 15 shows a design of a process 1500 for data transmission withtarget termination selection in a wireless communication system. Process1500 may be performed by a first station, which may be a relay station,a base station, or some other entity. The first station may determine atarget termination for a packet based on ACK transmission opportunitiesavailable to a second station for the packet (block 1512). The firststation may select a modulation and coding scheme (MCS) for the packetbased on the target termination for the packet (block 1514). The firststation may transmit the packet in accordance with the selected MCS tothe second station (block 1516).

In one design, ACK information for the packet can be sent in subframesof an interlace. The ACK transmission opportunities may correspond tosubframes belonging in the interlace and allocated for use. In onedesign, the target termination for the packet may be determined based ona first ACK transmission opportunity for the packet, e.g., as shown bythe last example in FIG. 12. In another design, the target terminationfor the packet may be K transmissions of the packet if K ACKtransmission opportunities are available for the packet, where K is aninteger greater than one.

In one design, transmissions of the packet may be sent at a firstperiodicity, and subframes at a second periodicity may be allocated foruse. The second periodicity may be different from the first periodicity.For example, the first periodicity may correspond to 8 ms, and thesecond periodicity may correspond to 10 ms.

In one design, the first station may be a base station, and the secondstation may be a relay station. In another design, the first station maybe a relay station, and the second station may be a UE. The first andsecond stations may also be some other combinations of base station,relay station, and UE.

FIG. 16 shows a design of an apparatus 1600 for data transmission withtarget termination selection in a wireless communication system.Apparatus 1600 includes a module 1612 to determine at a first station atarget termination for a packet based on ACK transmission opportunitiesavailable to a second station for the packet, a module 1614 to select amodulation and coding scheme (MCS) for the packet based on the targettermination for the packet, and a module 1616 to transmit the packet inaccordance with the selected MCS from the first station to the secondstation.

FIG. 17 shows a design of a process 1700 for transmitting data in ashortened subframe in a wireless communication system. Process 1700 maybe performed by a first station, which may be a relay station, a basestation, a UE, or some other entity. The first station may determine asubframe to send data to a second station (block 1712). The firststation may determine a part of the subframe used by the second stationto transmit control information (block 1714). The first station maytransmit data to the second station in the remaining part of thesubframe (block 1716). In one design, the first station may select anMCS based on transmission of the data in only the remaining part of thesubframe instead of the entire subframe. The first station may thenprocess the data in accordance with the selected MCS.

In one design, the subframe may comprise a control portion and a dataportion. The data may be transmitted in (i) the entire data portion ifthe second station is not transmitting control information in thesubframe or (ii) only part of the data portion if the second station istransmitting control information in the subframe. In one design, thetiming of the first station may be offset by N symbol periods relativeto timing of the second station, where N may be one or greater. Theoffset of N symbol periods may be selected to avoid overlapping ofcontrol information and reference signal sent by the first station withcontrol information and reference signal sent by the second station.

In one design, the first station may be a base station, and the secondstation may be a relay station. In another design, the first station maybe a relay station, and the second station may be a base station. In yetanother design, the first station may be a UE, and the second stationmay be a relay station. The first and second stations may also be someother combinations of base station, relay station, and UE.

FIG. 18 shows a design of an apparatus 1800 for transmitting data in ashortened subframe in a wireless communication system. Apparatus 1800includes a module 1812 to determine a subframe to send data from a firststation to a second station, a module 1814 to determine a part of thesubframe used by the second station to transmit control information, anda module 1816 to transmit data from the first station to the secondstation in remaining part of the subframe.

FIG. 19 shows a design of a process 1900 for operation in a wirelesscommunication system. Process 1900 may be performed by a station, whichmay be a relay station, a base station, a UE, or some other entity. Thestation may determine a first partition of downlink resources into (i)backhaul downlink resources available for a base station to transmit toa relay station and (ii) access downlink resources available for therelay station to transmit to UEs (block 1912). The station may determinea second partition of uplink resources into (i) backhaul uplinkresources available for the relay station to transmit to the basestation and (ii) access uplink resources available for the UEs totransmit to the relay station (block 1914). The station may communicateon the downlink and uplink resources in accordance with the first andsecond partitions (block 1916).

The first partition may be based on a first ratio between the backhauldownlink resources and the access downlink resources. The secondpartition may be based on a second ratio between the backhaul uplinkresources and the access uplink resources. For asymmetric partition, thesecond ratio may be different from the first ratio.

In one design, the station may be a relay station. For block 1916, therelay station may receive first data on the backhaul downlink resourcesfrom the base station and may send ACK information for the first data onthe backhaul uplink resources to the base station. The relay station maysend second data on the access downlink resources to a UE and mayreceive ACK information for the second data on the access uplinkresources from the UE. In another design, the station may be a basestation. For block 1916, the base station may send data on the backhauldownlink resources to the relay station and may receive ACK informationfor the data on the backhaul uplink resources from the relay station.

The resources may comprise subframes. The first partition may comprisebackhaul downlink subframes and access downlink subframes. The secondpartition may comprise backhaul uplink subframes and access uplinksubframes.

In one design, the access downlink subframes may comprise subframes 0and 5 of each radio frame comprising ten subframes 0 through 9. Variousconfigurations may be supported. In a first configuration (e.g.,configuration 1A in Table 2), the backhaul downlink subframes maycomprise subframes 4 and 9, the backhaul uplink subframes may comprisesubframes 3 and 8, the access downlink subframes may comprise subframes0, 1, 5 and 6, and the access uplink subframes may comprise subframes 2and 7. In a second configuration (e.g., configuration 2A in Table 2),the backhaul downlink subframes may comprise subframes 3 and 9, thebackhaul uplink subframes may comprise subframe 7, the access downlinksubframes may comprise subframes 0, 1, 4, 5, 6 and 8, and the accessuplink subframes may comprise subframe 2. In a third configuration(e.g., configuration 3 in Table 2), the backhaul downlink subframes maycomprise subframes 7 and 9, the backhaul uplink subframes may comprisesubframe 2, the access downlink subframes may comprise subframes 0, 1,5, 6 and 8, and the access uplink subframes may comprise subframes 3 and4. In a fourth configuration (e.g., configuration 4 in Table 2), thebackhaul downlink subframes may comprise subframes 6, 7 and 9, thebackhaul uplink subframes may comprise subframe 2, the access downlinksubframes may comprise subframes 0, 1, 4, 5 and 8, and the access uplinksubframes may comprise subframe 3. Other configurations may also besupported.

FIG. 20 shows a design of an apparatus 2000 for operation in a wirelesscommunication system. Apparatus 2000 includes a module 2012 to determinea first partition of downlink resources into backhaul downlink resourcesavailable for a base station to transmit to a relay station and accessdownlink resources available for the relay station to transmit to UEs, amodule 2014 to determine a second partition of uplink resources intobackhaul uplink resources available for the relay station to transmit tothe base station and access uplink resources available for the UEs totransmit to the relay station, and a module 2016 to communicate on thedownlink and uplink resources in accordance with the first and secondpartitions.

The modules in FIGS. 16, 18 and 20 may comprise processors, electronicsdevices, hardware devices, electronics components, logical circuits,memories, software codes, firmware codes, etc., or any combinationthereof.

FIG. 21 shows a block diagram of a design of base station/eNB 110, relaystation 120, and UE 130. Base station 110 may send transmissions to oneor more UEs on the downlink and may also receive transmissions from oneor more UEs on the uplink. For simplicity, processing for transmissionssent to and received from only UE 130 is described below.

At base station 110, a transmit (TX) data processor 2110 may receivepackets of data to send to UE 130 and other UEs and may process (e.g.,encode and modulate) each packet in accordance with a selected MCS toobtain data symbols. For HARQ, processor 2110 may generate multipletransmissions of each packet and may provide one transmission at a time.Processor 2110 may also process control information to obtain controlsymbols, generate reference symbols for reference signal, and multiplexthe data symbols, the control symbols, and reference symbols. Processor2110 may further process the multiplexed symbols (e.g., for OFDM, etc.)to generate output samples. A transmitter (TMTR) 2112 may condition(e.g., convert to analog, amplify, filter, and upconvert) the outputsamples to generate a downlink signal, which may be transmitted to relaystation 120 and UEs.

At relay station 120, the downlink signal from base station 110 may bereceived and provided to a receiver (RCVR) 2136. Receiver 2136 maycondition (e.g., filter, amplify, downconvert, and digitize) thereceived signal and provide input samples. A receive (RX) data processor2138 may process the input samples (e.g., for OFDM, etc.) to obtainreceived symbols. Processor 2138 may further process (e.g., demodulateand decode) the received symbols to recover control information and datasent to UE 130. A TX data processor 2130 may process (e.g., encode andmodulate) the recovered data and control information from processor 2138in the same manner as base station 110 to obtain data symbols andcontrol symbols. Processor 2130 may also generate reference symbols,multiplex the data and control symbols with the reference symbols, andprocess the multiplexed symbol to obtain output samples. A transmitter2132 may condition the output samples and generate a downlink relaysignal, which may be transmitted to UE 130.

At UE 130, the downlink signal from base station 110 and the downlinkrelay signal from relay station 120 may be received and conditioned by areceiver 2152, and processed by an RX data processor 2154 to recover thecontrol information and data sent to UE 130. A controller/processor 2160may generate ACK information for correctly decoded packets. Data andcontrol information (e.g., ACK information) to be sent on the uplink maybe processed by a TX data processor 2156 and conditioned by atransmitter 2158 to generate an uplink signal, which may be transmittedto relay station 120.

At relay station 120, the uplink signal from UE 130 may be received andconditioned by receiver 2136, and processed by RX data processor 2138 torecover the data and control information sent by UE 130. The recovereddata and control information may be processed by TX data processor 2130and conditioned by transmitter 2132 to generate an uplink relay signal,which may be transmitted to base station 110. At base station 110, theuplink relay signal from relay station 120 may be received andconditioned by a receiver 2116, and processed by an RX data processor2118 to recover the data and control information sent by UE 130 viarelay station 120. A controller/processor 2120 may control transmissionof data based on the control information from UE 130.

Controllers/processors 2120, 2140 and 2160 may direct operation at basestation 110, relay station 120, and UE 130, respectively.Controller/processor 2120 may perform or direct process 1500 in FIG. 15,process 1700 in FIG. 17, process 1900 in FIG. 19, and/or other processesfor the techniques described herein. Controller/processor 2140 mayperform or direct process 1500, 1700 or 1900 and/or other processes forthe techniques described herein. Controller/processor 2160 may performor direct process 1500, 1700 or 1900 and/or other processes for thetechniques described herein. Memories 2122, 2142 and 2162 may store dataand program codes for base station 110, relay 120, and UE 130,respectively.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

Headings are included herein for reference and to aid in locatingcertain sections. These headings are not intended to limit the scope ofthe concepts described therein under, and these concepts may haveapplicability in other sections throughout the entire specification.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of wireless communication by a relaystation, the method comprising: communicating with a base station onbackhaul subframes and with a user equipment (UE) on access subframes;selecting an initial access subframe for a packet; finding a subframe,corresponding to the initial access subframe, for an acknowledge (ACK)of the packet, according to a predefined hybrid automatic retransmission(HARM) time line; determining whether the corresponding ACK subframe isa backhaul subframe; incrementing a value of a target termination forthe packet if the corresponding ACK subframe is not a backhaul subframe;selecting a modulation and coding scheme (MCS) for the packet based onthe target termination for the packet; and scheduling a transmission ofthe packet on the initial access subframe according to the selected MCS.2. The method of claim 1, further comprising: incrementing the value ofthe target termination if the corresponding ACK subframe is a backhaulsubframe, wherein ACK for the packet is delayed until a next ACKsubframe which is an access subframe.
 3. The method of claim 1, whereinthe initial access subframe is a downlink subframe from the relaystation to the UE, and the corresponding ACK subframe is an uplinksubframe from the UE to the relay station.
 4. The method of claim 1,wherein the predefined HARQ time line comprises an interlace withinwhich a data subframe is separated from its corresponding ACK subframeby a fixed number of subframes.
 5. A relay station, comprising: atransmitter and a receiver, configured to communicate with a basestation on backhaul subframes and with a user equipment (UE) on accesssubframes; a memory; and at least one processor coupled to the memoryand configured to: select an initial access subframe for a packet; finda subframe, corresponding to the initial access subframe, for anacknowledge (ACK) of the packet, according to a predefined hybridautomatic retransmission (HARQ) time line; determine whether thecorresponding ACK subframe is a backhaul subframe; increment a value ofa target termination for the packet if the corresponding ACK subframe isnot a backhaul subframe; select a modulation and coding scheme (MCS) forthe packet based on the target termination for the packet; and schedulea transmission of the packet on the initial access subframe according tothe selected MCS.
 6. The relay station of claim 5, wherein the at leastone processor is further configured to: increment the value of thetarget termination if the corresponding ACK subframe is a backhaulsubframe, wherein ACK for the packet is delayed until a next ACKsubframe which is an access subframe.
 7. The relay station of claim 5,wherein the initial access subframe is a downlink subframe from therelay station to the UE, and the corresponding ACK subframe is an uplinksubframe from the UE to the relay station.
 8. The relay station of claim5, wherein the predefined HARQ time line comprises an interlace withinwhich a data subframe is separated from its corresponding ACK subframeby a fixed number of subframes.
 9. An apparatus, comprising: means forcommunicating with a base station on backhaul subframes and with a userequipment (UE) on access subframes; means for selecting an initialaccess subframe for a packet; means for finding a subframe,corresponding to the initial access subframe, for acknowledge (ACK) ofthe packet, according to a predefined hybrid automatic retransmission(HARQ) time line; means for determining whether the corresponding ACKsubframe is a backhaul subframe; means for incrementing a value of atarget termination for the packet if the corresponding ACK subframe isnot a backhaul subframe; means for selecting a modulation and codingscheme (MCS) for the packet based on the target termination for thepacket; and means for scheduling a transmission of the packet on theinitial access subframe according to the selected MCS.
 10. The apparatusof claim 9, further comprising: means for incrementing the value of thetarget termination if the corresponding ACK subframe is a backhaulsubframe, wherein ACK for the packet is delayed until a next ACKsubframe which is an access subframe.
 11. A non-transitorycomputer-readable medium having instructions stored thereon, theinstructions comprising codes executable to cause an apparatus to:communicate with the base station on backhaul subframes and with a userequipment (UE) on access subframes; select an initial access subframefor a packet; find a subframe, corresponding to the initial accesssubframe, for acknowledge (ACK) of the packet, according to a predefinedhybrid automatic retransmission (HARM) time line; determine whether thecorresponding ACK subframe is a backhaul subframe; increment a value ofa target termination for the packet if the corresponding ACK subframe isnot a backhaul subframe; select a modulation and coding scheme (MCS) forthe packet based on the target termination for the packet; and schedulea transmission of the packet on the initial access subframe according tothe selected MCS.
 12. The non-transitory computer-readable medium ofclaim 11, further comprising codes to: increment the value of the targettermination if the corresponding ACK subframe is a backhaul subframe,wherein ACK for the packet is delayed until a next ACK subframe which isan access subframe.